Perhaps I misunderstand you, but looking at the evidence we see that Tolkien never wrote about Sauron raising orcs from the dead. Why then should such an invention be made in a film, when the orcs clearly fill a very different purpose in Middle Earth than being a supernatural enemy? If the film makers wanted more supernatural, undead enemies, they can use creatures from Norse folk tales, which fit Tolkien's world better than typical zombies, like Barrow-wights.

The Barrow-wights are the only creatures described that really fit the bill of creatures similar to zombies. I don't agree that Nazgūl and Barrow-wights are the same either. The Nazgūl are men who end up being controlled by Sauron through their possession of The Nine rings, who live beyond their span because of their Rings, and who devote themselves to sorcery and black arts and gradually become more and more ensnared by Sauron's deceits and phantoms. When speaking about the Nazgūl, it's most helpful IMO to look at what Tolkien wrote about how a Ring of Power affects mortals ("The shadow of the past" and to look at what Aragorn and Gandalf says about their nature ("A knife in the dark", "Many meetings") and what is written about their origin in The Silmarillion. It's true that the Nazgūl don't live in the waking world like ordinary people do and are not alive in the ordinary sense, but they have never actually died and then been re-animated from the grave either.

But anyway all of this is very theoretical since we do not know anything about what will actually be in the film. I don't even know if there will be an undead Azog or Nazgūls rising from crypts or in what context we will see it, so I'll just treat these unconfirmed rumours for what they are for the present.